Merlin, the wise wizard from King Arthur's time, served to protect and guide. He was the prophet of the Holy Grail, he told Uther Pendragon to establish a knightly fellowship (the Round Table), and he assured Uther that his true heir (Arthur) would be revealed as the one who could draw the sword from the stone. What a difference a few centuries makes!
Today, MERLIN conjures up wizardly images all right, except these images spell fear and cost to the mailing industry. But with a little effort, you can easily turn MERLIN into an ally, a competitive advantage, a way to confidently provide your customers with a service that separates you from the pack.
What is MERLIN?
Although you've read it a hundred times before, it's important to note that MERLIN is more than a measure of barcode print quality. It also has to do with the layout of the piece, the location of the text and barcode. MERLIN looks at PostNet bar heights and widths, ink splatter (extraneous ink present), voids (gaps between dots forming the bars), slanted symbols (tilt), skewed print, reflectance (darkness of the bars, lightness of the background) plus several other categories. You could produce the perfect barcode on a piece and still fail MERLIN because you positioned the PostNet code too low or too close to the edge. These are areas that require manual intervention and inspection a low-level, periodic quality check is your best defense.
There are three main types of inkjet printers you'll most likely use to print MERLIN-inspected pieces. They are single-nozzle continuous inkjet (CIJ; this also includes an "upgraded" version of ganged-together CIJs, where a single housing contains multiple CIJs), thermal inkjet (HP-based products) and binary array. Each technology offers strengths and weaknesses in terms of its ability to print MERLIN-conforming PostNet symbols.
CIJ technology works by applying an electrical charge to a droplet of ink. The drops are then deflected accordingly to create various alphanumeric characters, graphics and barcodes. The typical benefit of this technology is the ability to print onto products moving at very high speeds. The inks, typically solvent-based methyl-ethyl ketone (MEK), provide fast-drying results on most substrates.
With CIJ technology, the biggest challenge to overcome is the limited resolution. Even "arrayed" CIJ (a cluster of single-nozzle jets in one housing), provides a limited number of dots to create the PostNet code. The keys to successful PostNet printing with a CIJ printer are maintenance and set-up. You must ensure you're getting the best possible print quality from the machine, and the way to do this is with good maintenance habits. You then need to make sure you have the unit set up properly, including the head mount, encoder if applicable, photo eye and transport. Also make sure the print is vertical; slanted print will result in a bar tilt problem. With the a
HP-based products utilize Thermal Ink Jet (TIJ) technology to effectively produce high-resolution images. This print technology uses heat to generate vapor bubbles, which "jets" small drops of ink through nozzles onto a substrate to form text or images. With optional operational resolutions from 75 to 600 dpi horizontal (with a fixed vertical dpi of 600), adjustments can be made to compensate for the porosity of the piece. The benefits of HP-based products and their corresponding high resolution eliminates potential too tall/too short bar errors, and symbol contrast, as with the other technologies, should not be an issue. However, with its limited ink offerings, you need to be sure the ink performs acceptably on the particular piece. Too much bleed and you will be out of spec because your bars are too wide.
Binary array technology is similar to continuous inkjet technology. Tiny drops of ink are deflected in flight by an electrostatic field. With binary technology, an array of individual jets (~256) are used to create a single print band. A charge electrode applies a charge to the ink drop, which is deflected. When no charge is applied the drop, is not deflected. The ink drops that are not used for printing are charged and deflected into the gutter. The uncharged drops are not deflected by the high voltage field and fly to the substrate to create the image. Because uncharged drops are used for printing, excellent print quality and high speeds (~1,000 feet per minute) can be achieved.
With binary array technology, you need to be aware of the ink performance on the particular piece. With a water-based array printer, you'll have potential ink bleed that, if not properly accounted for, will produce failing PostNet symbols. Conversely, as with CIJ printers and fast-drying inks, an MEK-based array printer may produce an ink droplet too small to form a passably wide enough bar.
A fourth emerging technology is high resolution UV-cure. The print engine utilizes Piezo-electric technology to produce high resolution images (300+ dpi) with a fast-drying UV-cure ink. The print engine contains a series of chambers that are filled with ink. By applying voltages to the walls of these chambers, a distortion is caused that bows the walls. This movement creates a space, drawing more ink into the chamber. When the voltage is released and the walls return to their original positions, an ink droplet is expelled through a selected nozzle. A UV lamp cures the print, producing a crisp, high-quality image. As with the other technologies, ink performance on the substrate is critical to assure a quality barcode. The added setup of the UV lamp also requires attention, to ensure you are getting the proper curing.
A Simple QC Plan
Nothing gets in the way of uptime. Except maybe a rejected job because it failed MERLIN. With a little effort, you can prevent costly run mistakes. As discussed earlier, a good portion of the MERLIN specification deals with the layout of the printed information. Obviously you want to confirm proper layout at the outset of the job. But what about during · the job? While checking every piece would prove costly and unrealistic, why not devise a time or piece interval to do a quality inspection on a single piece? For example, if you are running a 100,000 piece run, perform piece quality checks at the 10,000s 10,000, 20,000, etc. Use a gauge to measure the PostNet symbol; check the positioning of the symbol; check print quality for overspray and dot connection. Ensure that, for the particular job, each aspect of the MERLIN spec is conforming. Make any necessary adjustments to bring yourself back to a maximum tolerance level.
Additionally, use a barcode reader to scan each symbol. A barcode reader simply attempts to decode the information in the symbol. It doesn't check the symbol for quality, positioning or contrast. While you won't get the verification that a postal barcode verifier provides, you will know that each piece has a readable code. And scanners are a much more affordable option; check out offerings from Microscan and Sick, to name a few. By checking 10 pieces, plus scanning each piece, you have a degree of assurance your job will pass MERLIN. The more frequent the quality checks, the higher the degree of confidence.
With a little setup wizardry of your own, you can turn MERLIN into a benevolent, positive force one that can offer you a competitive advantage against those who choose to fight the otherwise all-powerful (and here-to-stay!) wizard.
Scott Liniger is a consultant in the imaging and auto-identification industry, with over 15 years of experience in the industrial coding and marking industry. Contact him at firstname.lastname@example.org.